Epoxy resins are organic substances or mixtures of organic substances which generally contain two or more (mostly isolated, generally terminal) epoxy groups per molecule and which can be cross-linked by reaction of those epoxy groups to form thermoset molding compositions. The formation of cured epoxy resins is known from the state of the art. A very common method for obtaining a suitable uncured epoxy resin is the very well known reaction of bisphenol-A with 2 moles of epichlorohydrin, which takes place in the presence of sodium hydroxide.

The epoxy resins of the bisphenol A/epichlorohydrin type—generally referred to as “bis-A-resins” represent of course the most common product, followed by bisphenol F/epichlorohydrin resins. Commercially available uncured epoxy resins generally have a relatively low molecular weight and are converted into high molecular weight materials by chemical reaction through the addition of a so-called hardener. Accordingly, the hardener promotes cross-linking therefore, it was originally proposed to refer to the epoxy resins before cross-linking as pre-condensates or intermediates rather than resins. However, this nomenclature has never been adopted. The expression “uncured epoxy resin” is now widely used for the straight resin while the expression “cured epoxy resin” is reserved for the cross-linked product.
For transforming the intermediates into the cured resins the oxirane rings are opened and, in many cases, the free valencies are attached to other functional groups present in the epoxy resin with incorporation of the hardener. Cross-linking takes place by polyaddition or polymerization without the elimination of solid, liquid or gaseous substances, so that bubble formation is avoided, even in the absence of pressure, and very little shrinking occurs. Numerous substances are known as suitable hardeners from the prior art, however, of particular importance are reactive amines, especially polyamines. The schema illustrates the reaction by a simple example of epoxy and amine reaction:

Usually di- or polyamines like e.g. diethylentriamine are used, thus one does not only obtain a linear molecule but a mixture of branched polymers, which are known as epoxyamine-adducts, some of them also called “waterpoxys”. For example, US 20050154091 A1 (Lohe et al.) describes a method of preparation of a water based epoxy resin curing agent in dispersion form which water based curing agent is formed by combining an active amine-hydrogen containing amine-functional dispersion (A) with an active amine-hydrogen containing amine-functional curing agent (B) in solution or emulsion form, wherein said active amine-hydrogen containing amine-functional dispersion (A) comprises a reaction product of a) a polyamine compound having at least three active amine-hydrogen, and b) an aqueous epoxy resin dispersion having an epoxy solids equivalent weight of equal to or greater than 150 g/eq, and wherein said active amine-hydrogen containing amine-functional curing agent (B) has a solids hydrogen equivalent weight of 50-500 g/eq; is capable of emulsifying a liquid epoxy resin to produce a stable emulsion.
Waterpoxys represent low molecular intermediates which are converted into the final products (“Cured Epoxy Resins”), which are useful as adhesives, coatings or flooring agents by reaction with uncured epoxy resins, optionally in the presence of hardeners, in particular short chain polyamines.
Mercaptan hardeners represent commercially available products and their advantages are e.g. described in the monography “Mercaptans: An added dimension of epoxy coatings” by S. Hartman and R. Dallago published by the company Henkel Corp., which is a summary of a lecture given at a symposium on Feb. 23, 1987. In particular, this paper shows that the product “Capcure” offers many advantages over conventional hardeners for epoxy resins. Cured epoxy resins obtained from waterpoxys and capcures are e.g. described in EP 0932648 B1, EP 1238028 B1, EP 1379597 B1, EP 1392784 B1, EP 1426347 A1, and EP 1426348 A1 (all Cognis) which in are hereby incorporated by reference.
A serious disadvantage, however, is that the cured epoxy resins represent solids and so far are not available as aqueous dispersions or emulsions, since they show a strong tendency to precipitate. Since on the other hand it would be highly desirable to apply said cured epoxy resins out of an aqueous composition the problem which underlies the present invention has been to modify the existing process for obtaining cured epoxy resins so that the resulting products can be offered in the form of emulsions or dispersions with at least comparable storage stability, while at the same time providing a better solvent resistance, a significant shorter gel time even at low temperature, no shrinkage, and more flexibility.